NSW racing authorities have demanded Melbourne Cup-winning trainer Darren Weir show cause why horses trained by him should be allowed to race in the state, after police said they seized electric-shock devices in raids on his Victorian stables yesterday.

Key points:

Police allegedly found four electric-shock devices in raids across several properties

The devices can be used to condition horses to run faster in response to a physical cue

Weir and two other men were released without charge while the police investigation continues

In a statement confirming it had issued Weir with a Show Cause Notice, Racing NSW noted Weir had nominated several horses for the Golden Slipper, which will be held at Rosehill Racecourse on March 23, and nominations were due soon for The Championships, which will be held at Royal Randwick in April.

Racing NSW said under Australia's racing rules, the use and possession of electronic devices such as jiggers was an offence which carried a mandatory minimum penalty of two years' disqualification.

"It is critical that the image, interests and integrity of thoroughbred racing in New South Wales are not compromised while Mr Weir's conduct is further investigated," Racing NSW chief executive Peter V'landys said.

Interviewed on ABC News Breakfast this morning, Racing Victoria chief executive Giles Thompson said yesterday's discovery of jiggers came as something of a surprise.

"The information that we're talking about with electrical devices only became apparent yesterday," Mr Thompson said.

"There's no evidence to suggest that [the use of jiggers] is widespread. However, if people are suggesting that it is, I would suggest that they contact the stewards or Victoria Police with any information that they have."

'A Pavlov's Dog response'

Herald Sun investigative journalist Andrew Rule said jiggers were used in training to give a "a small but effective shock" to a horse, and this "slightly unpleasant experience" can be used to trigger a faster performance on race day.

'It's imperative … we get this right'

Mr Thompson said the police and stewards were still assessing information and intelligence collected yesterday, and it was unclear if or when any charges would be laid.

"We understand that people want us to take action and take the next steps as soon as we possibly can, and we will," he said.

"But we need to make sure that we get that right.

Who is Darren Weir?

Born in the town of Berriwillock in Victoria's north-west

Left school at 15 and began work in the horse-racing industry

Took out his own trainer's licence aged 25, when based at Stawell

Expanded operations to Ballarat and Warrnambool as his success grew

Won 348 races in the 2015-16 season, setting a new Commonwealth training record

Trained the 2015 Melbourne Cup winner Prince of Penzance

"The teams that were executing those warrants, and the Racing Victoria stewards who were in attendance with Victoria Police, didn't complete [the job] until yesterday afternoon.

"It is absolutely imperative for the integrity of our sport and for the equine welfare in our sport that we get this right."

He said Racing Victoria could sanction anyone using a jigger on a horse.

Australian Trainers Association chief executive Andrew Nicholl said while the situation was "unsavoury", it shows the programs to crack down on wrongdoing are working.

"It's a ringing endorsement for the integrity structure and the manner in which the authorities go about policing the sport and making it a level playing field for everybody," he told ABC Radio Melbourne.

"There will [always] be an element who are prepared to push the envelope. My message to the general public is let's not define the sport by the actions of the few."